This invention relates in general to communications equipment. More particularly, it is directed to providing a communication device with the ability to switch or arbitrate between a plurality of communication buses.
An electronic card chassis typically provides a plurality of card slots for inserting electronic equipment or application cards. Typically, these application cards are designed to perform a variety of communication functions such as providing a modem card or other communication interface card capability. In addition to application cards capable of performing a variety of communication functions, the electronic card chassis may also contain a management card to perform system overhead management functions for the application cards in the chassis.
In the electronic card chassis, a communication backplane provides the application cards a source of power and communication access to other application cards in the card chassis. The communication backplane may include a plurality of different communication buses to allow electronic circuit cards in the card chassis to communicate to external devices or to other cards in the card chassis.
In particular embodiments of an electronic card chassis, a dedicated communication bus allows the management card to communicate to the plurality of application cards. This management communication bus provides management cards a dedicated communication path to access each of the application cards in the card chassis.
Today, digital computer networks implemented using these types of electronic card chassises are carrying a larger amount of communications including data and voice. Increasingly critical applications such as banking financial transactions now use this type of equipment to implement communication. Thus, the need for reliability and fault tolerant equipment has increased. To provide for fault tolerant operation, the card chassis may include a number of management cards for backup and redundancy in case of a failure of a primary management card. If a primary management card were to experience a failure, a second or backup management card could take over the management function of the application cards in the electronic card chassis. Similarly, the card chassis may provide a plurality of redundant management communication buses in the case of failure of a communication bus.
In this redundant configuration including a plurality of management cards, each of the plurality management cards will typically have a backplane communication bus connection to each of the application cards. As a result of the plurality of management cards and the redundant communication buses, each application card will have a plurality of backplane communication buses from which it may receive communications from the management cards at any time. As a consequence, the application card must be capable of receiving messages from any of the management cards over any one of the backplane communication buses accessing the card. Thus, to properly receive incoming management messages from any of the management cards, the application card must be able to dynamically switch between different backplane communication buses.
In accordance with an illustrative embodiment of the present invention, problems associated with managing communications from a plurality of different communication buses are addressed. The present embodiment allows application cards to arbitrate between messages on a plurality of different communication buses from devices communicating to the application card.
According an embodiment of the invention, application cards may arbitrate between messages on a plurality of different communication buses from devices communicating to the application card.
In the illustrative embodiment, the application card includes an arbiter that monitors the plurality of communication buses to determine which communication bus is current accessing the application card. To this end, the arbiter monitors when a communication bus becomes active. When it detects a communication bus is active and no other mutually exclusive bus is active, the arbiter will allow that communication bus to access the application card. The communication bus can be switched to access the local bus of the application card. Once a communication bus is allowed access to the communication card, a hold off signal may be given to other communication buses accessing the application card. In addition, a timer may be utilized with the present embodiment to prevent a device from holding the communication bus to the application card for too long a period of time. It should be understood that the application card may be simultaneously accessed by a number of communication buses while other communication buses utilize mutually exclusive (one-at-a-time) access to the application card.
According to another aspect of the present invention, the arbiter allows the application card to dynamically select or arbitrate between different communication buses. The arbiter may include state machine logic to implement appropriate protocol of the communication bus. The arbiter can employ a variety of different algorithms to allow and control access to the application card. The arbiter may allow access to the application card according to the priority of different communication buses. The arbiter can allow simultaneous access to the application card according to the types and classes of different communication buses. Using the present invention, any arbitrary scheme for selecting among a plurality of communication buses may be implemented and dynamically tailored and changed according to the needs of the particular device.
In another illustrative embodiment, the application card includes a physical layer interface capable of switching between redundant physical buses providing communication to the application cards. To provide fault-tolerant operation, the equipment card chassis in this embodiment provides a plurality of redundant physical buses to carry information to the application cards. The redundant physical buses provide backup capability for fault-tolerant operation in the case of failure of a physical bus. During such a failure, the application card may switch from one physical bus to another backup redundant bus. In the illustrative embodiment, the physical bus is a 10-Base-2 Ethernet bus that is dedicated for carrying management information to application cards in an equipment card chassis. The 10-base-2 bus includes redundant physical buses.
According to another aspect of the invention, a physical layer bus interface switches the active physical bus between redundant physical buses according to a dynamic criterion. In an embodiment of the invention, a second bus carries the criterion that indicates the currently active physical bus communicating to the application card. In the exemplary embodiment, the second bus is utilized to carry a criterion bit that determines the active physical bus. An expander breaks out the criterion bit to the physical layer bus interface to switch the appropriate physical bus. Based on the criterion, physical interface switch selects the appropriate physical bus.
The described embodiments provide devices and methods enabling reliable fault tolerant communication platforms. The ability to automatically select between redundant hardware and software allows backup equipment to be provided and dynamically utilized as needed without taking the platform out of service. The foregoing and other features and advantages of an illustrative embodiment of the present invention will be more readily apparent from the following detailed description, which proceeds with references to the accompanying drawings.